1. Field of the Invention
The invention relates to a clamping element for setting or fixation of a bone fracture as well as to a setting or fixation device comprising such a clamping element.
2. Discussion of Background Information
When a bone fracture is immobilized insufficiently, a callus formation, i.e. a tyloma-like thickening of the ends of the fracture from overgrowing bone tissue, can occur. In order to avoid such an indirect fracture healing via a callus, bone plates are used which are applied and attached to the outer surface of a broken bone so that the fracture site is set, i.e. fixed, during the healing process.
For such applications for the treatment of bone fractures, from prior art there are mainly known rigid, metallic bone plates formed in a planar manner and having bores which are screwed at the opposite sides of a fracture. For the fastening of such settings or fixations, usually so-called cortical screws are used which are screwed into the outer bone tissue, the so-called cortical layer, which has the highest strength of the bone. The setting or fixation ensures that the ends of the fracture cannot move with respect to each other and that newly formed bone tissue can accumulate such that it will not be subjected to any loads.
Furthermore, it is assumed that the healing process of a fracture can be influenced beneficially when a compression is applied onto the joined fracture site. Thereby, a particularly close adaption, i.e. a very small clearance over which the ends of the fracture grow towards each other again, is effected.
In order to obtain said desired function, the published patent application US 2008/0154312 A1 discloses a two-part bone plate, the two halves of which can move towards each other by means of an axial guide. For the creation or production of a compression, in various embodiments a band-shaped elastomeric member is provided which is stretched around the halves.
The published patent application US 2007/0293863 A1 describes a bone bridge having two plate-shaped elements for receiving bone screws through which an elastic cable extends.
Such simple constructions of elastic bone plates or bridges have the disadvantage that the pretension cannot be readjusted. If necessary, a stepwise adaptation can be provided by a staggered selection of elastic elements of different lengths or different stress-strain curves. An exact adaptation of the pretension with respect to dimensional tolerances of fastening points, however, is impossible.
A defined pretension is of importance with regard to the coordination of several settings, in particular of mutually opposing settings, as well as with regard to indifferent fracture margins, in order to ensure an exact alignment of the fracture ends with respect to each other during the entire healing process.
Accordingly, when the above-mentioned devices are used, the fixing means have to be placed into the bone in a surgical operation very accurately as regards position. Furthermore, due to the course of the fracture lines and due to the anatomic conditions, in practice the distance of the fixing means is not always freely selectable.
Furthermore, a system with an elastic principle of action, i.e. with a distinctive stress-strain curve, will always exhibit the following disadvantages:
The relationship between that pretension which is required for an effective fixing of the position against external forces acting thereupon and that force which acts upon the fracture ends for the adaption due to the same pretension is directly dependent on the stress-strain curve of the used elastic element. In other words, for an effective setting or fixation of fracture sites onto which, due to anatomic conditions, a large leverage acts during body movements, as is for instance the case for tubular bones at the arms or the legs, a correspondingly high pretension is required in order to reliably prevent a deflection of the fracture site by potential forces acting thereupon.
Said pretension of an elastic element, which is determined by its function, will, however, permanently apply a possibly unfavourably high pressure onto the bone tissue of the fracture site.
In this connection, elastic elements with a correspondingly short and steep stress-strain curve have more favourable properties with respect to the pretension for a compression and their suitability for the fixing in a stable position. On the other hand, they are more sensitive to dimensional tolerances of the fastening points. Rigid bone plates uncouple said two properties so that a desired compression of the ends of the fracture fails to appear.
Therefore, the invention is based on the object to provide a clamping element for a setting or fixation device, which clamping element provides a very good and stable fixing of the position against outer forces as well as an adjustable compression of the fracture which can be adapted individually to fastening points which are conditioned by the fracture or by the anatomy, and which can nevertheless be produced at particularly low costs, in order to expand the field of application of compression-producing settings. Moreover, the invention is also based on the object to provide a setting or fixation device in which the clamping element is used.